With Crossfire, all monitors need to be plugged into the first video card. NONE of the outputs on the second GPU work while in Crossfire mode. (With SLI, the outputs on both GPUs work.)

If a game doesn't support Crossfire it should still run in eyefinity mode as eyefinity is not crossfire dependant. Most games that won't run crossfire are likely gonna have issues with eyefinity however. Although I'm sure there are some out there that will manage it.